Spectra generator for test and calibration

ABSTRACT

A spectra generator having an electrically programmable diffraction grating. There may be a broad band light source that emits light which is diffracted by the grating. Diffracting elements in the grating may be individually adjustable so that generation of a specific spectrum or spectra may be achieved. The diffracting elements may be adjusted according to electrical signals of a program from a computer. The generated synthetic spectra may be used for testing and calibration of spectrometers or other devices. Synthetic spectra may also be used for scene generation and other purposes.

BACKGROUND

The present invention pertains to spectra and particularly infraredspectra of various substances. More particularly, the invention pertainsto the generation of synthetic spectra and use of such spectra intesting and calibration of spectrometers.

The invention may be related to U.S. Pat. No. 5,905,571, by Butler etal. issued May 18, 1999, and entitled “Optical Apparatus for FormingCorrelation Spectrometers and Optical Processors”; U.S. Pat. No.5,757,536, by Ricco et al., issued May 26, 1998, and entitled“Electrical-Programmable Diffraction Grating; and U.S. Pat. No.6,664,706, by Hung et al., issued Dec. 16, 2003, and entitled“Electrostatically-Controllable Diffraction Grating”; which are hereinincorporated by reference. The invention may also be related to U.S.patent application Ser. No. 10/352,828, by Hocker, filed Jan. 28, 2003,and entitled “Programmable Diffraction Grating Sensor”; and U.S. patentapplication Ser. No. 09/877,323, by Hocker et al., filed Jun. 8, 2001,and entitled “Apparatus and Method for Processing Light”, which areherein incorporated by reference.

SUMMARY

The invention may be an apparatus and method for the testing andcalibration of spectrometers using generated synthetic spectra. Thesegenerated synthetic spectra may be used for other purposes such as scenegeneration.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic of a spectra generator having an electricallyprogrammable reflective diffraction grating;

FIG. 2 is an intensity versus wavelength graph of radiation from anexample black body;

FIG. 3 is an example spectrum that may represent the absorption ofinfrared light by a particular substance;

FIG. 4 is a diagram of an actual spectrum of HF, a simulated spectrum ofHF and a displaced simulated spectrum of HF;

FIG. 5 is a diagram of an actual spectrum of TCE, a simulated spectrumof TCE and a modified simulated spectrum of TCE; and

FIGS. 6 a and 6 b show end and top views, respectively, of anelectrically adjustable grating.

DESCRIPTION

Spectrometers may be used to detect molecules in the atmosphere byobserving the characteristic spectra of light absorbed by the molecules.Such spectrometers should be tested and calibrated with spectra thatresemble the target molecules. Creating test spectra by using samples ofthe molecules, such particular species of them, may be inconvenient,time consuming and expensive. Additionally, using samples of the actualmolecules may be hazardous if the species are toxic. Specifically,military systems used for standoff chemical agent detection needcapabilities for test and calibration with actual spectral inputrepresenting the chemical agents to be detected, but without the need touse samples of actual toxic chemical agents.

In FIG. 1, a generator 10 of spectra is shown. A light source 11 mayoutput light 12 of a black body, that is, broadband infrared light. Alens 13 may collimate light 12 for impingement on a diffractive grating14. Electrically programmable diffractive grating 14 may reflectbroadband light 12 as spectra light 15. The design may insteadincorporate a transmissive grating in lieu of the reflective grating.The reflective grating may be generally referred to here.

Spectra light 15 may be detected by a spectrometer 16. Light 15 may be asynthesization of a light spectrum resulting from absorption by aspecific substance. If spectrometer 16 is functioning properly, then itmay identify that that spectrum light 15 to be that of the specificsubstance. The light 15 beam width may be adjusted with a beam expanderor beam compressor so that light 15 is more effectively transmitted anddetected by spectrometer 16.

The electrically programmable diffraction grating 14 may transformbroadband light 12 into spectra light 15 in accordance with a dimension,such as the height of diffraction elements 17, relative to the base ofdiffractive gating 14. These dimensions of electrically programmablediffraction grating 14 in the Figures are not drawn to scale but areillustrative. The actual number of elements 17 may be over 1000, e.g.,1024. Also, angle 18 may be a factor affecting the synthesized spectra15. The spectra of light 15 generated may be a function of the heightsof the elements 17 and of angle 18 of the direction of diffracted light15 relative to the direction of incident light 12 impinging grating 14.Each element 17 may have a unique height.

The heights of the elements 17 may be adjusted in order to generatevarious spectra in diffracted light 15. The heights of the diffractiveelements 17 may be set with electrical signals from a computer 19 via aconnection 21 to an interconnection base 22 attached to grating 14.Computer 19 may be programmed to provide ready-made settings for theelements 17 to generate specific spectra of respective substances.Background about an electrically programmable diffraction grating may bedisclosed in U.S. Pat. Nos. 5,905,571 and 5,757,536, and U.S. patentapplication Ser. No. 09/877,323.

For instance, if a request is input to computer 19 for a spectrum of CO,than an element pattern may be sent to grating 14 which may result in anadjustment of elements 17 so as to result in a spectrum of CO being indiffracted light 15 sent to a receptor 16 such as a spectrometer.Elements 17 may be adjusted so as to reflect light 15 having spectra ofmore than one substance. Also, background may be added to the spectra oflight 15. Spectrometer 16 may be tested with the reception of light 15to determine detection capability of various substances among variousbackgrounds. Device 16 may be tested for identifying a spectrum of aparticular substance or several substances buried in noise at one levelor another. Computer 19 may provide spectra settings to elements 17 in asequential fashion over a given period of time. Spectra for calibrationof spectrometer 16 or other instrumentation may be provided via light15. Further, a detection mechanism may be used added to device 16 toidentify and verify the spectra being used for testing and calibratingspectrometers and the other instrumentation. Also, spectra may begenerated for scene generation and the testing and/or calibration ofmicrobolometers and other detection mechanisms.

FIG. 2 is a graph of intensity versus wavelength of infrared light.Curve 31 reveals a spectrum of black body source which may be lightsource 11 of generators 10 and 20. However, source 11 may emit otherwavelengths of the like, such in the ranges of visible or UV light. FIG.3 is an example of a spectrum 32 of light 15 or 24 after the light 12 istransmitted through a region containing a specific molecule. Light maybe absorbed in spectral wavelengths in a pattern characteristic of thatmolecule.

FIG. 4 shows a graph of three spectra of HF. The top spectrum may beregarded as an actual spectrum curve 51 of HF. Curve 52 may be asynthetic spectrum of HF as provided by spectra generator 10 or 20.Curve 53 is the same as curve 52 except that it is shifted to the rightabout 50 wave numbers. If the spectrum 52 is compared with the actual HFspectrum 51, and spectrum 52 is delayed periodically to the position ofspectrum 53, spectrum 51 may be easier to detect when a comparison isdone for calibrating the generator. Generators 10 and 20 may generateboth a spectrum 52 and a displaced spectrum 53 of HF. This spectradisplacement shifting may accommodate AC detection of an actualspectrum.

FIG. 5 shows an actual spectrum 61 of TCE and a synthetic spectrum 62 ofTCE. Spectrum 62 may be provided by generators 10 and 20. Anotherprovided spectrum 63 may effectively be spectrum 62 of TCE with the 850cm⁻¹ absorption line removed by generator 10 or 20 due to an adjustmentof the elements 17 in diffractive grating 14 or 23, respectively.

FIGS. 6 a and 6 b show aligned end and top views of the adjustablegrating 14 that may be used in generator 10. A basic structure of thisadjustable grating 14 may be like that of grating 23, except thatgrating 23 may have a transparent property rather than a reflective one.Elements 17 may be pulled down electrostatically by elements 71. Onepolarity of a voltage source may be connected to all of the elements 17at support 73. The other polarity of the voltage source may be connectedto an individual element 71 positioned relative to its correspondingelement 17. Elements 17 may be like flexible tongs that have a naturalresting position close structure 72 and a fixed structural connection tostructure 73. A magnitude of a voltage applied across element 17 and 71may determine the position of element 17 relative to element 71. Thegreater the voltage magnitude, element 17 may be drawn closer to element71. Thus, all elements 17 may be individually adjusted to achieve aparticular and unique diffractive grating 14 setting for providing adesired spectrum from generator 10. The voltage inputs to elements 71may be individual and different from one another. The base 74 isinsulated so that elements 71 may be electrically isolated from oneanother and connected to an external signal source such as computer 19.The various sets of voltage inputs with their respective combinations ofmagnitudes may be programmed in computer 19. The positions of elements17 and consequently grating 14 may be dynamically changed in a manner toget the effect of going from spectrum 52 to spectrum 53 of FIG. 5 orfrom spectrum 62 to spectrum 63 of FIG. 6.

Although the invention has been described with respect to at least oneillustrative embodiment, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentspecification. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. An apparatus comprising: a diffracting mechanism having a pluralityof adjustable elements; and wherein: the adjustable elements have setpositions to provide certain spectra upon impingement of radiation onthe diffracting mechanism; and the certain spectra may be used forcalibration and/or test of a spectrometer.
 2. The apparatus of claim 1,wherein the certain spectra may be detected at specific angles relativeto a direction of the impingement of radiation on the diffractingmechanism.
 3. A broadband generator comprising: a light source; and alight diffracting mechanism, having adjustable elements, proximate tothe light source; and wherein: the elements are adjusted to diffractlight from the light source as a specific spectrum or spectra; and thespecific spectrum or spectra may be used to calibrate and/or test aspectrometer.
 4. The generator of claim 3, wherein the light source mayemit infrared light.
 5. The generator of claim 3, further comprising acomputer connected to the light diffracting mechanism.
 6. The generatorof claim 5, wherein the computer may provide signals to the lightdiffracting mechanism for adjusting the elements.
 7. The generator ofclaim 6, wherein the computer has sets of signals that representspecific substances in that such sets of signals sent to the lightdiffracting mechanism may result in the elements being adjusted so as toprovide spectra of the specific substances.
 8. The generator of claim 7,wherein the light diffracting mechanism has a reflective grating.
 9. Thegenerator of claim 7, wherein the light diffracting mechanism hastransmissive grating.
 10. The generator of claim 3, further comprisingcollimating optics situated between the light source and the lightdiffracting mechanism.
 11. The generator of claim 3, further comprising:a detection mechanism situated in a path of spectra provided by thelight diffracting mechanism; and wherein: the detection mechanism has anadjustable angle of position relative to the light diffractingmechanism; and a changing of the adjustable angle of position affectscharacteristics of the spectra detected by the detection mechanism. 12.The generator of claim 11, wherein the detection mechanism may identifyand/or verify the spectra from the light diffracting mechanism.
 13. Aspectra generator comprising: a light source; and a light diffractingmechanism, having adjustable elements, proximate to the light source;and wherein the elements are adjusted to diffract light from the lightsource as a specific spectrum or spectra; and the specific spectrum orspectra may be used for emanating a scene.
 14. The generator of claim13, wherein the scene is for testing a detector.
 15. The generator ofclaim 14, wherein the light source may emit infrared light.
 16. Thegenerator of claim 15, wherein the detector is a bolometer.
 17. Meansfor generating spectra, comprising: means for diffracting radiation;means for providing the radiation to the means for diffractingradiation; means for adjusting the means for diffracting radiation toprovide various kinds of spectra; and means for conveying the variouskinds of spectra to a spectrometer for testing the spectrometer.
 18. Themeans of claim 17, further comprising means for conveying the variouskinds of spectra to the spectrometer for calibrating the spectrometer.19. The means of claim 17, further comprising a means for programmingconnected to the means for adjusting the means for diffractingradiation.
 20. The means of claim 19, wherein the means for programmingprovides various settings to the means for adjusting to attain specificspectra from the means for diffracting radiation.
 21. The means of claim20, wherein the radiation is infrared.
 22. The means of claim 20,wherein the radiation is broadband light.
 23. A method for generatingspectra, comprising: providing radiation; and adjustably diffracting theradiation into spectra; conveying the spectra to a spectrometer; andtesting the spectrometer to see if it appropriately detects the spectra.24. The method of claim 23, further comprising calibrating thespectrometer relative to the spectra.
 25. The method of claim 23,further providing a plurality of sets of adjustments for adjusting thediffracting the radiation into specific spectra corresponding to each ofthe sets of adjustments, respectively.
 26. The method of claim 23,further comprising: providing a mechanism for detecting the spectra toverify an output of appropriate spectra; and wherein the mechanism isplaced at an adjustable angle relative to a direction of the radiation.